The mass and energy balance of sea ice are strongly connected through the transfer of solar radiation from the atmosphere through snow and sea ice into the ocean. Recent studies show that a major uncertainty in quantification of the sea ice mass balance is related to the timing and duration of the melt season as well as the very limited knowledge of the characteristics of the snow layer on top. Therefore, we are working on (1) improving our understanding of radiative transfer into and through Arctic and Antarctic sea ice and its impacts on sea-ice melt, and (2) improving existing and developing new remote sensing tools and data products. This allows for estimates of sea-ice melt and freeze rates, and large-scale estimates of heat fluxes in and under sea ice. Here we show established methods for melt onset detection on sea ice based on passive microwave data, and we present first new ideas for future improvements for onset detection methods.